The present invention relates in general to combination locks, and more particularly to view limiting dial and dial ring assemblies for combination locks to afford security against unauthorized observation of the combination being dialed when opening the lock.
It has long been recognized that the dialing combination for combination locks are subject to theft by unauthorized viewing of the successive registrations of dial markings occurring during opening of the lock. Where such a lock is opened in the presence of other persons, it is a simple matter for each persons to note the combination from a point to the side of or at angles to the rear or over the shoulder of the operator and thereby gain unauthorized access to the vault, safe or other security receptacle protected by the lock. Even where some restriction of the field of view is achieved, persons do not have to see the entire combination dialed at one time, but can learn one number each time the unauthorized observer is able to look at the dial when the combination is being dialed by an authorized person, and thus over a short period of time acquire knowledge of the dialling combination without arousing suspicion of the authorized person opening the safe. Ideally, the dial should expose the indicia or numbers of the combination actually being run only to the authorized operator and not anyone standing elsewhere.
Heretofore, various expedients have been proposed for use in connection with conventional combination lock dials, which shield the greater portion of the dial from view by unauthorized persons. These have generally taken the form of a shield or cover provided with a window exposing only a limited number of the dial markings to view, either from a direction forwardly of the dial, or in some cases from a direction above the dial where the dial markings and numerals are merely provided on a peripheral cylindrical flange surface of the dial. Such dial shields have the dual purpose of tempering observation of the dial numbers by possible surreptitious observance to either side of the operator while the operator is dialing the combination, and limiting the range of exposed dial markings which are visible so that the body of the operator will shield the exposed dial area from observation by persons at remote locations or to the side of the operator. Earlier U.S. Pat. Nos. 2,728,215 to Bremer, 2,858,692 to Deaton et al, and 2,836,052 to Harry C. Miller, one of the joint inventors of this application, are typical of such prior structures. Such prior art dial shields, however, were usually in the form of additional accessories which must be associated with the combination lock and dial, and in many cases afford such a limited visible dial area that the lock dial must be operated very slowly in order to bring the proper numbers on the dial into registry with the index, zero or reference mark. Also because of the restricted visible dial area, the numbers are often so obscure or difficult to count that the operator must make a number of attempts before the successful combination is dialed. U.S. Pat. No. 2,690,664 to Harry C. Miller, and U.S. Pat. No. 4,197,726 to Uyeda are examples of combination lock dial and ring assemblies having a limited range of visibility forwardly of the dial, also for the purpose of reducing the chance of unauthorized viewing of the combination while it is being dialed by an authorized operator.
An object of the present invention is to provide a view limiting dial and dial ring assembly for combination locks and the like adapted to be mounted on vertical safe doors or similar vertical surfaces, which more severely limits the angular range of viewing positions in reflected light ray paths from which an authorized operator can dial the combination of the associated combination lock mechansim, further reducing the chance of unauthorized observation of the lock combination when being dialed.
Another object of the present invention is the provision of a novel view limiting dial and dial ring assembly for combination locks and the like as described in the preceding paragraph, wherein the numeral markings on the dial are provided on the rearwardly facing surface of the dial as mirror image numerals of normal dial marking numerals and are observable only by reflection from a reflective mirror surface rearwardly confronting the marked dial portion observable from a highly restricted range of observation points to the front and above the dial.
Another object of the present invention is the provision of a novel and ring assembly for combination locks and the like as described in the two immediately preceding paragraphs, wherein the index, zero or reference mark for the dial is provided as an opaque thin planiform vane member intercepting observation of portions of the forwardly visible dial markings from side locations.
Another object of the present invention is the provision of a novel dial and dial ring assembly for combination locks useable in view limiting installations as described in the preceding paragraphs and also interchangeable with members to provide restricted forward viewing of the dial without using reflective ray paths to observe dial markings.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating preferred embodments of the invention.